Synthetic biology of cyanobacterial cell factories

In the field of microbial biotechnology rational design approaches are employed for the generation of microbial cells with desired functions, such as the ability to produce precursor molecules for biofuels or bioplastics. In essence, that is the introduction of a (new) biosynthetic pathway into a microbial cell to create a ‘microbial catalyst’. Utilizing cyanobacteria as production hosts has the potential to contribute to a bio-based economy. Cyanobacteria are prokaryotes that perform oxygenic photosynthesis. By ‘re-programming’ their metabolic network their photosynthetic metabolism can be used to synthesize valuable products from CO2, sunlight and water, O2 being the only by-product. Compared to traditional biofuel production this direct production would bypass the need to initially synthesize complex ‘biomass’ which has to be broken down again in later steps.
Key to the work presented in this thesis is the optimization of synthetic pathways, which are introduced into the cyanobacterium Synechocystis sp. PCC 6803 by means of genetic engineering. The carbon metabolism, originating from the fixation of CO2, is ‘tapped’ for the production of carbon-based compounds such as lactic acid, butanediol, and ethanol. The introduced biosynthetic pathways, which are originating from chemotrophic organisms, result in a trade-off between production and growth due to the ‘re-channeling’ of the carbon flux of the metabolism. Undoubtedly, different factors contribute to the success of a well-engineered cyanobacterial production strain. General knowledge about regulatory networks and also experience with metabolic engineering of cyanobacteria is still at the beginning.